In production of semiconductor wafers, the back of a semiconductor wafer with IC elements formed thereon is generally polished to make the wafer as thin and uniform as possible. For example, the thickness of the wafer is decreased from about 0.5 mm to from about 0.2 to 0.3 mm by such a polishing.
Various techniques have been employed to prevent the breakage of the semiconductor wafer or damage of the wafer surface: (a) a method comprising coating a paint on the surface of the wafer to form a coating, polishing the back of the wafer and removing the coating with a solvent, (b) a method comprising laminating a thin sheet on the surface of the wafer as a spacer, polishing the back of the wafer and removing the sheet, and (c) a method comprising applying a pressure-sensitive thin adhesive sheet to the surface of the wafer, polishing the back of the wafer and peeling off the thin adhesive sheet.
In cutting and separating the semiconductor wafer into IC element chips, a method comprising forming wedge-shaped grooves of low depth on the surface of the semiconductor wafer in conformity with the shape of the desired IC chip and dividing the semiconductor wafer into the IC element chips by applying an external force has been employed. This method, however, has disadvantages in that the separation accuracy is poor, and productivity is low since the IC element chips after cutting and separating must be transferred to the subsequent mounting step by the hand.
For this reason, the direct pick-up method has now been employed, comprising fixing the semiconductor wafer by bonding thereto a thin adhesive sheet, cutting the assembly into the IC element chips by means of a rotary blade and picking up the IC element chips from the thin adhesive sheet while simultaneously mounting the chips.
In the above direct pick-up method, the semiconductor wafer is washed with water under a hydraulic pressure of at least 2 kg/cm.sup.2 to remove friction heat and scraps during cutting the semiconductor wafer with the rotary blade. Thus, it is required for the thin adhesive sheet to have a sufficient adhesive force to withstand the hydraulic force. If, however, the adhesive force is too large, it is difficult for the IC element chips to be removed from the thin adhesive sheet. For this reason, the adhesion force of the thin adhesive sheet is controlled so as to be capable of withstanding the above hydraulic pressure but not to lower the efficiency of the pick-up operation.
However, the adhesive force of the thin adhesive sheet can be controlled as described above only when the size of the final IC element chip is up to about 20 mm.sup.2. In the case of IC element chips having a size of 50 mm.sup.2 or more as a recent LSI permit an increased degree of accumulation, it is difficult for the thin adhesive sheet to control the adhesive force as described above, and the above-described direct pick-up method cannot be applied.